1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to improvements of a package structure of a resin encapsulated-type semiconductor device which is formed by means of a TAB (tape automated bonding) system using a tape carrier.
2. Description of the Invention
FIG. 1 is a cross-sectional view illustrating a package structure of a semiconductor device produced by a conventional TAB system. FIG. 2 is a cross-sectional view illustrating the package of the semiconductor device shown in FIG. 1 which has warped after resin encapsulation. In these drawings, a semiconductor element 1 with an electrodes 2 provided thereon is mounted on an electrically conductive cap 5 by means of a first adhering member 7. A lead 4 is connected to the electrode 2. This lead 4 is formed of, for instance, a copper foil having a thickness of 35 .mu.m and comprises an inner lead portion 4a supported on a support tape 3, which serves an insulating film, and an outer lead portion 4b formed on an outer end portion of the support tape 3 and projecting toward the outside for connection to an external circuit (not shown). The inner lead portion 4a and the outer lead portion 4b are formed by being plated with Au or Sn after the carrier tape is laminated with a copper foil and a lead pattern is formed by photo-etching. The conductive cap 5 is formed by drawing a sheet formed of, for instance, a iron-nickel alloy with a thickness of 0.1 mm and by plating the drawn sheet with Ag. The rear surface of the semiconductor element 1 is adhered to a recess of the conductive cap 5 by means of the first adhering member 7, such as solder or a conductive adhesive. When the rear surface of the semiconductor element 1 requires a certain potential, the conductive cap 5 serves as an electrical path therefor, and when the semiconductor device operates, the conductive cap 5 serves as a heat radiating surface. The support tape 3 is supported by a collar 6 of the conductive cap 5 and is formed by stamping out a carrier tape which is similar to the one mentioned above and is formed of a 125 .mu.m-thick polyimide film used as a cinema film and provided with perforations. The support tape 3 is provided with a through hole 8, and a conductive member 8a formed by plating or the like is disposed in this through hole 8. By means of this conductive member 8a, a connecting pattern (not shown) of the lead 4 for supplying a rear-surface potential to the semiconductor element 1 and a conductive sheet 11 formed by laminating the rear surface of the support tape 3 with, for instance, a 35 .mu.m-thick copper foil and by subjecting the same to photo-etching. The collar 6 and the conductive sheet 11 are bonded to each other by means of a second adhering member 10. When a solder ring is used as the second adhering member 10, a bent end portion 12 of the conductive cap 5 facilitates positioning thereof, and when a conductive adhesive is used, the portion 12 prevents the adhesive from leaking out. The conductive cap 5, the semiconductor element 1, connecting portions thereof, etc. are covered with an encapsulating resin 9 such as epoxy resin for the purpose of protection.
A conventional semiconductor device is arranged as described above, and in order to assemble this semiconductor device, the carrier tape is first provided with required perforated portions to form the support tape 3. Patterns of the leads 4 and the conductive sheet 11 are formed on the obverse and reverse sides of this support tape 3. The conductive member 8a is disposed in the through hole 8 of the support tape 3, and the connecting pattern of the leads 4 for supplying a rear-surface potential to the semiconductor element 1 is connected to the conductive sheet 11 by means of this conductive member 8a. Furthermore, the tip portion of the inner lead portion 4a is aligned with the electrode 2 of the semiconductor element 1, and the electrode 2 and the inner lead 4a are heated and contact bonded to each other using a bonding tool.
Subsequently, square-shaped solder rings, which are used as the first and second adhering members 7, 10, are respectively disposed on the collar 6 and the bottom 5a of the conductive cap 5, or a conductive adhesive is applied thereto. Then, the semiconductor element 1 and the support tape 3 are positioned on the adhering members 7, 10. The solder rings are simultaneously heated and hardened, or portions of the conductive adhesive applied to the parts mentioned above are simultaneously heated and hardened, thereby simultaneously effecting bonding between the conductive cap 5 and the semiconductor element 1 and between the collar 6 and the conductive sheet 11. Subsequently, with the support tape 3 and the collar 6 of the conductive cap 5 clamped together, encapsulation with the encapsulating resin 9 is effected, thereby completing a semiconductor device.
In the above-described semiconductor device, since the edge portion of the conductive cap is shaped into the form of a collar, the mechanical strength of the edge portion of the conductive cap is weak. Accordingly, there has been a drawback in that, as shown in FIG. 2, the semiconductor device can warp due to the stress resulting from hardening and shrinkage of the encapsulating resin 9, with the result that excessive stress is applied to the semiconductor element 1, which is undesirable for good operation and reliability of the semiconductor device.